Corrosion resistant magnesium alloy

ABSTRACT

According to aspects of the present disclosure, a method includes obtaining a first amount of magnesium, a second amount of manganese, and a third amount of a cathodic poison and combining the magnesium, the manganese, and the cathodic poison to thereby form a kinetically hindered magnesium alloy includes less than 1 part by weight of manganese and less than about 5 parts by weight of cathodic poison based on 100 parts of the kinetically hindered magnesium alloy. The cathodic poison is configured to inhibit a cathodic reaction when combined with the magnesium.

TECHNICAL FIELD

The disclosure relates to the field of magnesium alloys and, morespecifically, to systems and methods for inhibiting corrosion ofmagnesium alloys.

BACKGROUND

Magnesium is a lightweight compound that can be used to form components.Magnesium-based components can be used in a variety of applications suchas housings and structural components in a variety of industriesincluding automotive, aerospace, and the like. These magnesium-basedcomponents can be, for example, structural components, enginecomponents, housings, high-temperature components, and the like.Beneficially, magnesium-based components are formed from the lighteststructural metal, provide for high-yield recycling, and providestructural features such as a grain structures that can be beneficialover alternative materials.

SUMMARY

It is desirable to produce magnesium-based components that are resistantto corrosion. Beneficially, methods of producing a kinetically hinderedmagnesium alloy disclosed herein can be used to form magnesium-basedcomponents. The kinetically hindered magnesium alloy is resistant tocorrosion and provides additional benefits as will be described furtherin the detailed description below.

According to aspects of the present disclosure, a method includesobtaining a first amount of magnesium, a second amount of manganese, anda third amount of a cathodic poison and combining the magnesium, themanganese, and the cathodic poison to thereby form a kineticallyhindered magnesium alloy includes less than 1 part by weight ofmanganese and less than about 5 parts by weight of cathodic poison basedon 100 parts of the kinetically hindered magnesium alloy. The cathodicpoison is configured to inhibit a cathodic reaction when combined withthe magnesium.

According to further aspects of the present disclosure, the cathodicpoison includes at least one element selected from the group consistingof periodic table of the elements Group 14 alloying elements, periodictable of the elements Group 15 alloying elements, and periodic table ofthe elements Group 16 alloying elements.

According to further aspects of the present disclosure, the cathodicpoison consists of silicon.

According to further aspects of the present disclosure, the cathodicpoison consists of a nonmetallic alloying element.

According to further aspects of the present disclosure, the cathodicpoison is a nonmetallic alloying element selected from the groupconsisting of phosphorous, sulfur, and selenium.

According to further aspects of the present disclosure, the cathodicpoison consists of at least one periodic table of the elements Group 16alloying element.

According to further aspects of the present disclosure, the first amountof magnesium includes a hydrogen promotor, and the hydrogen promotor isnot removed prior to or during forming the kinetically hinderedmagnesium alloy.

According to further aspects of the present disclosure, further includesexposes the kinetically hindered magnesium alloy directly to an aqueousenvironment.

According to further aspects of the present disclosure, further includesforming an automobile component from the kinetically hindered magnesiumalloy.

According to aspects of the present disclosure, a method includesobtaining a first amount of magnesium, a second amount of manganese, anda third amount of a cathodic poison and combines the magnesium, themanganese, and the cathodic poison to thereby form a kineticallyhindered magnesium alloy includes less than about 6 parts by weight of acombination of the manganese and the cathodic poison based on 100 partsby weight of the kinetically hindered magnesium alloy. The cathodicpoison is configured to inhibit a cathodic reaction when combined withthe magnesium.

According to further aspects of the present disclosure, the cathodicpoison consists of silicon.

According to further aspects of the present disclosure, the cathodicpoison consists of a nonmetallic alloying element.

According to further aspects of the present disclosure, the cathodicpoison is a nonmetallic alloying element selected from the groupconsisting of phosphorous, sulfur, and selenium.

According to further aspects of the present disclosure, the cathodicpoison consists of a periodic table of the elements Group 16 alloyingelement.

According to aspects of the present disclosure, a method includesobtaining a first amount of magnesium, a second amount of manganese, anda third amount of a cathodic poison and combining the magnesium, themanganese, and the cathodic poison to thereby form a kineticallyhindered magnesium alloy. The cathodic poison is a nonmetallic alloyingelement is configured to inhibit a cathodic reaction when combined withthe magnesium.

According to further aspects of the present disclosure, the kineticallyhindered magnesium alloy includes less than about 6 parts by weight of acombination of the manganese and the cathodic poison.

According to further aspects of the present disclosure, the kineticallyhindered magnesium alloy includes less than 1 part by weight of themanganese and less than about 5 parts by weight of the cathodic poison.

According to further aspects of the present disclosure, the nonmetallicalloying element is selected from the group consisting of phosphorous,sulfur, and selenium.

According to further aspects of the present disclosure, further includesexposes the kinetically hindered magnesium alloy directly to an aqueousenvironment.

According to further aspects of the present disclosure, further includesforming an automobile component from the kinetically hindered magnesiumalloy.

The above features and advantages and other features and advantages ofthe present disclosure are readily apparent from the following detaileddescription.

DETAILED DESCRIPTION

Magnesium-based products corrode when exposed to aqueous environments.The corrosion proceeds through a cathodic reaction. The corrosionreaction for water contacting a magnesium substrate can be expressed asfollows.

Mg+2H₂O→Mg(OH)₂+H_(2(g))   (1)

The anodic half-reaction can be expressed as follows.

Mg→Mg²⁺+2e ⁻  (2)

The cathodic half-reaction can be expressed as follows.

H⁺ +e ⁻→H_((ad))   (3)

Adsorbed hydrogen H_((ad)) produced by the cathodic half-reaction,equation (3), remains adsorbed to a first active site of the magnesiumsubstrate until another adsorbed hydrogen H_((ad)) occupies a secondactive site of the magnesium substrate that is near enough to the firstactive site to allow the two adsorbed hydrogen H_((ad)) atoms to evolvegaseous diatomic hydrogen H₂.

Beneficially, according to aspects of the present disclosure, magnesium,manganese, and a cathodic poison can be combined to form a kineticallyhindered magnesium alloy that is configured to inhibit the cathodicreaction to thereby inhibit hydrogen evolution and corrosion ofmagnesium-based products formed from the kinetically hindered magnesiumalloy. A cathodic poison is any element or combination of elements thatkinetically inhibits the cathodic reaction. In some aspects, thecathodic poison is configured to inhibit the cathodic reaction whencombined with the magnesium. The cathodic poison can kinetically inhibitthe cathodic reaction by altering the number of sites available for thecathodic reaction to occur, increase distances between sites for thecathodic reaction to occur, combinations thereof, and the like.

In some aspects, the cathodic poison includes alloying elements fromperiodic table of the elements Groups 14-16. As used herein, “alloyingelements” refers to elements that are capable of forming an alloy withmagnesium either alone or in combination with other elements. Periodictable of the elements Group 14 alloying elements include, for example,silicon, germanium, tin, and lead. Periodic table of the elements Group15 alloying elements include, for example, phosphorous, arsenic,antimony, and bismuth. Periodic table of the elements Group 16 alloyingelements include, for example, sulfur, selenium, tellurium, andpolonium.

In some aspects, the cathodic poison is silicon. Surprisingly, siliconcan be used as the cathodic poison to inhibit to inhibit the cathodicreaction and the generation of gaseous hydrogen when alloyed withmagnesium. Beneficially, silicon is more abundant, less expensive,easier to process and purify by known methods in industries such asmicroelectronics manufacturing, and less dangerous to handle andincorporate than metallic poisons such as mercury, indium, and gallium.

In some aspects, the cathodic poison is a nonmetallic alloying element.Surprisingly, nonmetallic alloying elements can be used as the cathodicpoison to inhibit the cathodic reaction and the generation of gaseoushydrogen when alloyed with magnesium. In some aspects, the cathodicpoison is a nonmetallic alloying element consisting of elements selectedfrom nonmetallic elements. More particularly, the nonmetallic alloyingelement can be selected from the group consisting of phosphorous,sulfur, and selenium. Beneficially, nonmetallic alloying elements can bemore abundant, less expensive, easier to process, and less dangerous tohandle and incorporate into the alloy than metallic poisons such asmercury, indium, and gallium.

In some aspects, the cathodic poison is an alloying element selectedfrom periodic table of the elements Group 16. Surprisingly, alloyingelements from periodic table of the elements Group 16 can be used as thecathodic poison to inhibit to inhibit the cathodic reaction and thegeneration of gaseous hydrogen when alloyed with magnesium.Beneficially, one or more alloying elements selected from periodic tableof the elements Group 16 can be used to enhance machinability and otherproperties of the resulting alloy.

In some aspects, a method of forming the kinetically hindered magnesiumalloy includes obtaining a first amount of magnesium, a second amount ofmanganese, and a third amount of cathodic poison. The first amount ofmagnesium may be obtained through, for example, obtaining commerciallypure magnesium (e.g., 99.8% Mg). Alternatively, the first amount ofmagnesium may be obtained through, for example, obtaining a magnesiumalloy consisting of magnesium and other compounds. Magnesium alloys usedto obtain the first amount of magnesium can include magnesium mixedwith, for example, aluminum, zinc, manganese, silicon, copper, rareearth elements, zirconium, combinations thereof, and the like. Someexample magnesium alloys suitable for obtaining the first amount ofmagnesium include AZ91 (about 9 parts by weight Al and about 1 part byweight Zn with the balance being substantially Mg), AZ92(about 9 partsby weight Al and about 2 parts by weight Zn with the balance beingsubstantially Mg), AZ63 (about 6 parts by weight Al and about 3 parts byweight Zn with the balance being substantially Mg), A10 (about 10 partsby weight Al with the balance being substantially Mg).

The method further includes combining the obtained magnesium, manganese,and cathodic poison to form the kinetically hindered magnesium alloythrough any suitable alloying process as would be recognized by one ofordinary skill in the art. In some aspects, the kinetically hinderedmagnesium alloy includes less than 1 part by weight of manganese andless than about 5 parts by weight of cathodic poison. In some aspects,the kinetically hindered magnesium alloy includes less than about 6parts by weight of manganese and cathodic poison. The balance of thekinetically hindered magnesium alloy is generally magnesium. In someaspects, the kinetically hindered magnesium alloy is about 88 parts byweight of magnesium. In some aspects, the kinetically hindered magnesiumalloy is at least 94 parts by weight of magnesium.

The materials used to obtain the first amount of magnesium generallyinclude at least one hydrogen promotor (such as iron, nickel, copper,cobalt, and the like) as a contaminant. The hydrogen promotercontributes to corrosion of the magnesium and components formedtherefrom. While the materials can be purified to minimize the at leastone hydrogen promotor, the at least one hydrogen promotor generallycannot be eliminated entirely. Thus, the at least one hydrogen promoterwill continue to promote the cathodic reaction. Beneficially, aspects ofthe present disclosure provide for forming kinetically hinderedmagnesium alloys that inhibit the cathodic reaction even in the presenceof the at least one hydrogen promotor. In some aspects, the hydrogenpromotor is not removed prior to or during forming the kineticallyhindered magnesium alloy. As such, costs associated with purification ofthe materials can be avoided while achieving significant corrosionresistance.

In some aspects, a magnesium-based component is formed from thekinetically hindered magnesium alloy. The magnesium-based component canbe, for example, an automobile component.

Some magnesium-based components have a protective coating applied tosurfaces of the components to prevent contact between an aqueousenvironment and a magnesium substrate of the magnesium-based component.These protective coatings can include at least one layer of material onthe surfaces of the magnesium-based components. Detrimentally, anydamage to the protective coating, such as a scratch that reaches themagnesium substrate, exposes magnesium within the magnesium substrate toan aqueous environment. As such, the coating can be rendered ineffectiveby contact or ordinary wear and weathering. Beneficially, aspects of thepresent disclosure provide for forming kinetically hindered magnesiumalloys that can be exposed directly to an aqueous environment withoutthe protective coating. Kinetically hindered magnesium alloys in accordwith the present disclosure continue to inhibit cathodic reactions aftera surface of the magnesium-based component is damaged or removed becausethe kinetically hindered magnesium alloy itself inhibits corrosion.Additionally, the surface coatings tend to be formed from expensivematerials such as noble metals. As such, costs associated with applyingprotective coatings to the magnesium-based components and obtainingmaterials for the protective coating can be avoided while achievingsignificant corrosion resistance.

Beneficially, forming components from the kinetically hindered magnesiumalloy results in magnesium-based components that are resistant tocorrosion. Further, these magnesium-based components formed from thekinetically hindered magnesium alloy provide a practical alternative tousing other materials, such as aluminum or steel, which can reduceoverall weight of the components, reduce costs of acquiring rawmaterials, reduce costs of manufacturing, reduce costs associated withrecycling of components, increase yield of recycled components, and/orreduce overall vehicle weight.

While the best modes for carrying out the disclosure have been describedin detail, those familiar with the art to which this disclosure relateswill recognize various alternative designs, embodiments, and aspects forpracticing the disclosure within the scope of the appended claims.

1. A method comprising: obtaining a first amount of magnesium, a secondamount of manganese, and a third amount of a cathodic poison, thecathodic poison configured to inhibit a cathodic reaction when combinedwith the magnesium; and combining the magnesium, the manganese, and thecathodic poison to thereby form a kinetically hindered magnesium alloyincluding less than 1 part by weight of manganese and less than about 5parts by weight of cathodic poison based on 100 parts of the kineticallyhindered magnesium alloy.
 2. The method of claim 1, wherein the cathodicpoison includes at least one element selected from the group consistingof periodic table of the elements Group 14 alloying elements, periodictable of the elements Group 15 alloying elements, and periodic table ofthe elements Group 16 alloying elements.
 3. The method of claim 1,wherein the cathodic poison consists of silicon.
 4. The method of claim1, wherein the cathodic poison consists of a nonmetallic alloyingelement.
 5. The method of claim 1, wherein the cathodic poison is anonmetallic alloying element selected from the group consisting ofphosphorous, sulfur, and selenium.
 6. The method of claim 1, wherein thecathodic poison consists of at least one periodic table of the elementsGroup 16 alloying element.
 7. The method of claim 1, wherein the firstamount of magnesium includes a hydrogen promotor, and wherein thehydrogen promotor is not removed prior to or during forming thekinetically hindered magnesium alloy.
 8. The method of claim 1, furthercomprising exposing the kinetically hindered magnesium alloy directly toan aqueous environment.
 9. The method of claim 1, further comprisingforming an automobile component from the kinetically hindered magnesiumalloy.
 10. A method comprising: obtaining a first amount of magnesium, asecond amount of manganese, and a third amount of a cathodic poison, thecathodic poison configured to inhibit a cathodic reaction when combinedwith the magnesium; and combining the magnesium, the manganese, and thecathodic poison to thereby form a kinetically hindered magnesium alloyincluding less than about 6 parts by weight of a combination of themanganese and the cathodic poison based on 100 parts by weight of thekinetically hindered magnesium alloy.
 11. The method of claim 10,wherein the cathodic poison consists of silicon.
 12. The method of claim10, wherein the cathodic poison consists of a nonmetallic alloyingelement.
 13. The method of claim 10, wherein the cathodic poison is anonmetallic alloying element selected from the group consisting ofphosphorous, sulfur, and selenium.
 14. The method of claim 10, whereinthe cathodic poison consists of a periodic table of the elements Group16 alloying element.
 15. A method comprising: obtaining a first amountof magnesium, a second amount of manganese, and a third amount of acathodic poison, the cathodic poison being a nonmetallic alloyingelement configured to inhibit a cathodic reaction when combined with themagnesium; and combining the magnesium, the manganese, and the cathodicpoison to thereby form a kinetically hindered magnesium alloy.
 16. Themethod of claim 15, wherein the kinetically hindered magnesium alloyincludes less than about 6 parts by weight of a combination of themanganese and the cathodic poison.
 17. The method of claim 15, whereinthe kinetically hindered magnesium alloy includes less than 1 part byweight of the manganese and less than about 5 parts by weight of thecathodic poison.
 18. The method of claim 15, wherein the nonmetallicalloying element is selected from the group consisting of phosphorous,sulfur, and selenium.
 19. The method of claim 15, further comprisingexposing the kinetically hindered magnesium alloy directly to an aqueousenvironment.
 20. The method of claim 15, further comprising forming anautomobile component from the kinetically hindered magnesium alloy.